All Forbidden Lore skills represent information proscribed or hidden from the average Imperial citizen. In many cases, it is a heinous crime to even possess such data and can quickly draw Inquisitorial attention (even if the possessor himself is working for an Inquisitor).
Forbidden Lore has several diﬀerent Specializations as listed below. These include all Common Lore and Scholastic Lore Specializations, as each area also has blasphemous and dangerous knowledge beyond what is generally known, or secrets the group obsessively keeps to itself:

Archaeotech

Knowledge of the great, lost tech devices of times past, and clues to their mysterious functions and purposes.

Chaos Space Marines

Information concerning those Adeptus Astartes who turned traitor, as well as the paths they embrace and the equipment they use.

Criminals

Information regarding organised groups that ﬂout the Emperor’s Law in the local sector, such as those engaging in the Faceless Trade of proscribed artefacts.

Daemonology

Terrible knowledge about some of the most infamous Warp entities and their twisted physical manifestations.

Heresy

Wisdom concerning acts and practices deemed anathema by the Imperium, plus the most contemptible heretics of history and their infamous and deplorable acts.

The Horus Heresy

The origins and history of the 10,000 year long struggle between the forces of the Ruinous Powers and the Imperium of Man.

Inquisition

Even for those who serve an Inquisitor, knowing too much about their masters can be dangerous. Citizens who chose to study the history and nature of the Inquisition’s authority often are exposed to information that can forever ruin their minds.

Mutants

The study of stable and unstable mutations within humanity, their cancerous inﬂuence and mutagenic development over time, and some of the studies and tomes on the topic.

Oﬃcio Assassinorum

This highly secretive agency exists to eliminate powerful, often singular threats to the Imperium, such as renegade planetary governors or apostate preachers. Thsoe who dare study the organisation may become familiar with their techniques and wargear.

Pirates

Knowledge of the scourges of the Warp lanes throughout the local sector, their tactics, infamous vessels, and notorious captains.

Psykers

Skill in identifying psykers, the eﬀects of their unnatural powers, their dangers, and the general extent of their capabilities.

The Warp

An understanding of the energy of the Immaterium, its interaction and interrelation with realspace, and how its tides and eddies aﬀect travel between the stars.

Xenos

Knowledge of the minor and major alien species known to the Imperium, the threat they pose to Mankind, and their general appearance. Denote which Xeno species is selected for this specialization.

Forbidden Lore (Xeno)

There are countless species of Xeno inhabiting the dark corners of the galaxy. A few of the more widespread are listed here:

Barghesi

Eldar, Asuryani or Craftworlder†

Eldar, Corsairs†

Eldar, Drukhari or Commorrite†

Eldar, Exodites†

Eldar, Harlequins†

Eldar, Ynnari†

Galg

Hrud

Jokaero

Lacrymole

Loxatl

Necron

Ork

Q'orl

Tarellian

Tau, Demiurg†

Tau, Kroot†

Tau, Tau†

Tau, Vespid†

Tyranid, Genestealer†

Tyranid, Swarm†

Slaugth

Sslyth

†Achieving Rank 1 in one FL: Xenos subgroup also provides Rank 1 in all other subgroups with the same base species.